1. Field of the Invention
The present invention relates to surface-coated cermet blade members, and particularly, those which exhibit excellent wear resistance in high-speed cutting operations and superior fracture resistance in interrupted cutting operations.
2. Prior Art
Known surface coated cermet blade members comprise:
a cermet substrate which consists, apart from unavoidable impurities, of a binder phase of one or more iron family metals such as cobalt (Co) or nickel (Ni), and a hard-dispersed phase of balance carbo-nitride represented by the formula (Ti,M) (C,N), wherein M denotes one or more elements selected from tantalum (Ta), niobium (Nb), vanadium (V), zirconium (Zr), tungsten (W), molybdenum (Mo) and chromium (Cr); and PA1 a hard coating of an average thickness of 0.5 to 20 .mu.m formed on the surface of the substrate, the hard coating being composed of a single layer of TiX or of Al.sub.2 O.sub.3, or of multiple layers of TiX or Al.sub.2 O.sub.3, wherein X denotes one or more elements selected from carbon (C), nitrogen (N), oxygen (O) and boron (B).
For example, Japanese Patent Application First Publication, Serial No. 53-131910 describes a cermet with a hard coating which has an average thickness of 0.5 to 20 .mu.m and is composed of a single layer of a titanium compound such as TiCO or TiCNO, or of Al.sub.2 O.sub.3, or of multiple layers of titanium compounds and/or Al.sub.2 O.sub.3. Another Japanese Patent Application First Publication, Serial No. 56-62960 describes a surface-coated cermet in which a hard coating, composed of a single layer of a titanium compound such as TiN or TiCN, or of Al.sub.2 O.sub.3, or of multiple layers of titanium compounds and/or Al.sub.2 O.sub.3, is deposited on the surface of the cermet substrate through a TiC intermediate layer containing binder phase constituents distributed therein. Yet another Japanese Patent Application First Publication, Serial No. 63-134654 describes a hard coating composed of a single layer of a titanium compound such as TiC, TiN or TiCN, or of multiple layers of titanium compounds, the titanium compounds being in the form of grains having an average particle size of no greater than 0.5 .mu.m. However, the surface coated cermets disclosed in these three references have the disadvantages that since the bonding strength between the hard coating and the cermet substrate is low, the hard coating is susceptible to separation, resulting in short tool life.
Furthermore, in Japanese Patent Application First Publication, Serial No. 2-4972, there is disclosed a surface coated blade member which comprises a cermet substrate having a surface portion composed only of hard-dispersed phase constituents, and has a hard coating deposited thereon, composed of a single layer of a titanium compound such as TiC, TiN or TiCN, or of multiple layers of titanium compounds. However, since no binder phase constituents exist in the surface portion of the cermet substrate, the blade member is susceptible to fracture.
Moreover, Japanese Patent Application First Publication, Serial No. 2-22455 discloses a surface coated cermet blade member which comprises a cermet substrate in which the ratio C/C+N is greater at the surface portion than at interior portions, and a hard coating which is composed of a single layer of a titanium compound such as TiC, TiN or TiCN, or of multiple layers of titanium compounds. However, this blade member is also inferior in fracture resistance because the carbon content is great at the surface portion.
Thus, although various types of surface-coated cermet blade members have been developed in recent years, their ability to withstand higher cutting speed and the increasingly severe demands of the interrupted cutting operations have not kept pace with the requirements imposed by attempts to reduce labor over head and to improve efficiency. The prior art cermet blade members as described above lack sufficient wear resistance during high-speed cutting operations and are not sufficiently resistant to fracturing during interrupted cutting operations, as a result of which, tool life is reduced.